1. Field of the Invention
The present invention relates to a method of manufacturing a reticule or an optical mask employed in fabricating semiconductor devices.
2. Description of the Related Art
In generating a mask for manufacture of a semiconductor device, two reticules are prepared, one for a device pattern, which is, for example, 10 times magnification of an LSI chip and another one, which is, for example, 10 times magnification of an alignment mark. The two reticules are prepared by the use of data of pattern of the semiconductor device such as LSI (hereinafter referred to as device pattern) and the alignment mark pattern data, which are respectively generated by a design tool such as CAD (Computer Aided Design). At the time of manufacturing the mask, the device pattern is optically shrunken to 1/10 from the reticule of device pattern and it is then exposed onto a chromium mask plate. Next, the alignment mask pattern shrunken to 1/10 is additionally exposed from the alignment mark reticule onto the chromium mask plate so as to generate a sheet of mask.
However, since the exposure is done twice using two reticules for the device pattern and the alignment mark, respectively, it is impossible to entirely prevent displacement between the device pattern and alignment mark on the chromium mask plate at the exposure, no matter how carefully the processing is conducted. Moreover, as explained above, since two reticules are required to manufacture a sheet of mask, a considerable number of procedures are necessary for manufacturing both the reticules, resulting in a problem that the manufacturing cost becomes high.
As a method of overcoming such problems, it has been proposed that the alignment mark data is combined in the device pattern data, the combined data is previously shrunken by a predetermined reduction factor, thereafter such data is converted to the exposure data and a reticule is manufactured by the use of such exposure data. However, in this case, the sizes of not only the device pattern but also the alignment mark are concurrently shrunken. On the other hand, the alignment mark and its position are originally set (i.e., prior to being shrunken) to an individual exposing apparatus. Therefore, the exposing apparatus cannot detect the shrunken alignment mark; accordingly, it cannot use such combined data. For this reason, it has been necessary to perform such a troublesome procedure as generating the alignment mark data, whose size is previously changed by calculation according to the shrinking ratio, and combining it with the device pattern data.